Reciprocating expander valve operating apparatus, system and method

ABSTRACT

The disclosure describes a method to operate a conventional 4 cylinder engine as an expander for any pressurized fluid (e.g., liquid, vapor, or gas). A poppet valve system is disclosed enabling upward lift of the inlet valve, with assist from cylinder compression pressure, together with downward lift from an exhaust valve, resulting in especially efficient expansion of fluid or gas in a thermodynamic power cycle. Further, it is described that a desmodromic valve operation system may be employed and provides essential guidance and opening closing actions for proper operation of the expander system.

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser. No. 61/553,666, entitled “RECIPROCATING EXPANDER VALVE OPERATING APPARATUS, SYSTEM AND METHOD”, filed Oct. 31, 2011, the entire contents of which are herein incorporated by reference in their entirety.

This application is also related to U.S. application Ser. No. 12/773,431, entitled “HEAT ENGINE WITH CASCADED CYCLES”, filed May 4, 2010, U.S. Provisional Application Ser. No, 60/719,327, entitled “PIEZOELECTRIC SELECTABLY ROTATABLE BEARING,” filed on Sep. 21, 2005, U.S. Provisional Application Ser. No. 60/719,328, entitled “SOLAR HEAT ENGINE SYSTEM,” filed on Sep. 21, 2005, U.S. application Ser. No. 11/512,568, entitled “SOLAR HEAT ENGINE SYSTEM,” filed on Aug. 30, 2006, and U.S. application Ser. No. 12/246,127, entitled “HEAT ENGINE IMPROVEMENTS,” filed on Oct. 6, 2008, U.S. application Ser. No. 12/773,431, the entire contents of each of which are herein incorporated by reference in their entirety.

BACKGROUND

This disclosure relates to the conversion of heat energy to another form of energy, e.g. mechanical energy. The disclosure further relates to such conversion where the heat energy source is concentrated solar energy or a low grade or waste heat source.

Several different types of heat engines have been used in practice to convert concentrated solar radiation to mechanical power, notably Stirling cycle engines and Rankine cycle engines, trilateral flash cycle engines, and engines of the type described in the patent applications incorporated by reference above.

Heat engines of various types type typically employ one or more expanders. Expanders are devices (e.g. turbine or piston devices) through which a high pressure gas is expanded to produce work. Because work is extracted from the expanding high pressure gas, for may expanders the expansion is approximated by an isentropic process (i.e., a constant entropy process). For example, in theoretical, conventional Rankine cycles, expansion of working fluid takes place under reversible adiabatic conditions.

Because expanders are employed in a wide variety of heat engine systems, it would be advantageous to provide an expander that operates with high efficiency (e.g. extracting work with an efficiency approaching the thermodynamic limit), while maintaining desirable features such as low manufacturing cost, robust performance, etc. Moreover, it would be advantageous to provide an expander design that can be adapted for use under a variety of input conditions, e.g., over a broad range of working fluid input pressures.

SUMMARY OF THE INVENTION

The inventors have realized that devices, systems, and methods may be provided for the execution of thermodynamic cycles or the generation of power using pressurized heated or unheated fluids of any description, in a manner wherein most of the available energy in the fluid under a strict thermodynamic definition of same may be converted to mechanical work in a manner approaching 100% conversion efficiency.

In some embodiments, an expander is provided which includes facilities for input of working fluid into an expansion chamber (e.g., cylinder) and egress of same, whilst reducing or minimizing fluid friction losses and also reducing or minimizing mechanical loading on valves, cam trains and other mechanical components used to regulate the flow of working fluid through the expander.

In one aspect, the present disclosure relates to using a reciprocating or piston and cylinder type engine to expand any pressurized gas or liquid which converts to gas or mixture of vapor and liquid, utilizing poppet type valves and with mechanisms which enable valve opening and closing to be carried out. Various embodiments may be adapted for operation at essentially any suitable inlet pressure value.

In one aspect, the system may include a set of valves which work in different directions, the inlet valve always opening outward away from the cylinder and piston contained therein, the other, the exhaust valve, opening inward or towards the piston. In various embodiments, this motion of the inlet valve in the opposite direction to the exhaust valve applies for multiple valve combinations, as well as single valves

In another aspect, a desmodromic (also knows as a “positive in both directions”) valve operating system may be used that enables mechanically operated inward and outward or up and down motion of both types of valves, inlet and exhaust. In some embodiments, the desmodromic system is free of the spring closure mechanisms present in many conventional internal combustion engine inlet and exhaust valves systems and as, will be described, reduces or minimizes valve train loading forces, in this particular context.

In another aspect, devices and techniques are described which partially or wholly utilize a cylinder compression pressure after exhaust stroke, higher then or equal to the inlet pressure, by design to partially or wholly carry out inlet valve lifting or upward opening action, thereby minimizing forces on cam trains and/or eliminating opening cams altogether.

In various embodiments, the devices and techniques described herein have the capability to provide an expander of high isentropic efficiency in the case of expansion of fluids, including supercritical fluids. This is in contrast to conventional rotating turbomachines, which typically do not cope well due to greater fluid friction losses and leakage losses. Various embodiments of the presently described expansion device may have the higher isentropic efficiency that available gas expanders, e.g., those below 1 MW in capacity.

In another aspect, the devices and techniques described herein may provide the capability, e.g., in a four cylinder configuration and with the same valve train but differences in timing, to act as a two or more stage expander where one or several high pressure cylinders exhaust into one or more low pressure cylinders, leading to a highly efficient gas expansion process.

In one aspect, a method is disclosed of operating a reciprocating expansion device, the expansion device including at least one expansion chamber with a reciprocating element, a inlet to the expansion chamber with at least one outward opening inlet valve, and an exhaust from the expansion chamber having at least one inward opening outlet valve, the method including: providing pressurized working fluid to the inlet; opening the inlet valve in the outward directed to deliverer pressurized working fluid to the expansion chamber to expand and to drive a motion of the reciprocating element; and opening the outlet valve in the inward direction to allow expanded working fluid to escape the expansion chamber to the exhaust.

Some embodiments include opening and closing the inlet and outlet valves using a desmodromic cam device, said cam device applying force during both opening and closing movements of the inlet and outlet valves.

In some embodiments, each of the inlet and outlet valves is opened and closed without the use of a spring closure mechanism.

Some embodiments include: using an exhaust stroke of the reciprocating element to drive expanded working fluid out through the outlet valve; and using pressure generated in the expansion chamber during the exhaust stroke to apply an outward force to the inlet valve to assist in opening the inlet valve. In some embodiments, the pressure generated in the expansion chamber during the exhaust is greater than the pressure at the inlet on a side external to the expansion chamber.

In some embodiments, the applied outward force on the inlet valve reduces an inlet valve cam opening force on a cam used to open the inlet valve.

Some embodiments include providing pressure in the cylinder to a required value by controlling of the point of closure of the exhaust valve.

In some embodiments the opening of the inlet valve is accomplished using only the outward force to the inlet valve, generated by a recompression pressure in the cylinder.

In some embodiments, the inlet valve does not have an associated opening cam.

In some embodiments, the inlet valve includes one or more mechanical latches. In some embodiments, the method includes: using at least one mechanical latch to hold the inlet valve in a stable open or a stable closed position during at least a portion of an operating cycle of the expansion chamber.

Some embodiments include, during a first portion of the operating cycle, using the internal pressure of the expansion chamber to move the inlet valve outward towards a fully open position; and using at least one mechanical opening latch to hold the in the fully open position.

Some embodiments include using the operation of the opening latch to provide a force which assists in moving the inlet valve towards the fully open position.

In some embodiments, the inlet valve includes a mechanical latch and a spring mechanism. In some embodiments, the method includes: during a first portion of an operating cycle of the expansion chamber, using the mechanical latch to maintain the inlet valve in a closed position; during a second portion of the operating cycle, releasing the latch, and using pressure inside the expansion chamber to open the inlet valve; and using the spring mechanism to return the inlet valve from the open position to the closed position.

In some embodiments, the inlet valve is opened using the pressure inside the expansion chamber without the assistance of a force from an opening mechanism located external to the expansion chamber.

In some embodiments, the inlet valve includes at least one electromagnet. In some embodiments, the method includes: controlling the electromagnet to actuate the inlet valve between a substantially stable open position and a substantially stable open position.

In some embodiments, the at least one electromagnet includes at least a first and a second electromagnets. In some embodiments, the method includes: switching the first electromagnet to an on state and the second electromagnet to an off state to maintain the inlet valve in the stable open position; and switching the first electromagnet to an off state and the second electromagnet to an on state to maintain the inlet valve in the stable closed position.

In some embodiments, the inlet valve includes an over-center toggle mechanism having a stable closed and a stable open position. In some embodiments, the method includes: during a first portion of the operating cycle of the expansion chamber, using the internal pressure of the expansion chamber to toggle the inlet valve from the stable closed position to the stable open position.

Some embodiments include: during a second portion of the operating cycle, using a mechanism external to the expansion chamber to toggle the inlet valve into the stable closed position.

In some embodiments, the mechanism external to the expansion chamber includes at least one selected from the list consisting of: a cam, a mechanical actuator, a hydraulic actuator, and an electromechanical actuator.

In some embodiments, the inlet valve includes a spring loaded cam driven toggle mechanism. In some embodiments, the method includes: placing the valve in a closed position by seating a valve body against a seal, thereby causing a build up of pressure in the inlet to the expansion chamber; and rotating a cam to drive the toggle mechanism to apply an opening force on the valve body to unseat it from the seal, thereby placing the expansion chamber in fluid communication with the inlet and causing a reduction in inlet pressure.

In some embodiments, the force applied on the cam by the toggle mechanism is less than 20%, 10%, 5%, 1%, or less (e.g., in the range of 0-30%, or any subrange thereof) of the opening force applied to the valve body by the toggle mechanism.

In some embodiments, the reciprocating expansion device includes: a primary expansion chamber with a primary reciprocating element, and a secondary expansion chamber with a secondary reciprocation element. In some embodiments, the method includes: using fluid exhausted from the primary expansion chamber to drive the operation of the secondary expansion chamber.

In some embodiments, the expansion chamber and reciprocating element include a cylinder with a piston.

In some embodiments, the reciprocating expansion device includes at least four piston cylinders.

Some embodiments include providing a supercritical working fluid to the inlet of the expansion chamber.

Some embodiments include implementing at least one thermodynamic trilateral flash cycle at least in part using the reciprocating expansion device.

Some embodiments include implementing at least two cascaded thermodynamic cycles at least in part using the reciprocating expansion device.

Some embodiments include using the reciprocating expansion device to extract mechanical work from expansion of the working fluid with an efficiency of at least 90%, 95%, 97%, or more (e.g. in the range of about 75% to about 100%, or any subrange thereof) of the thermodynamic limit.

Some embodiments include using the reciprocating expansion device to do work at the rate of at least 0.1, 0.5. 1.0, or 10.0 megawatts (e.g. in the range of 0.01-100 megawatts or any subrange thereof).

In another aspect, an apparatus including a reciprocating expansion device is disclosed, the apparatus including: at least one expansion chamber with a reciprocating element, an inlet to the expansion chamber with at least one outward opening inlet valve and configured to receive a pressurized working fluid, an exhaust from the expansion chamber having at least one inward opening outlet valve; and a valve drive system. In some embodiments, the valve drive system is configured to: open the inlet valve in the outward directed to deliver pressurized working fluid to the expansion chamber to expand and to drive a motion of the reciprocating element; and open the outlet valve to allow expanded working fluid to escape the expansion chamber to the exhaust.

In some embodiments, the valve drive system includes a desmodromic cam device, said cam device applying force during both opening and closing movements of the inlet and outlet valves.

In some embodiments, during operation, each of the inlet and outlet valves is opened and closed without the use of a spring closure mechanism.

In some embodiments, where the expansion device is configured to: use an exhaust stroke of the reciprocating element to drive working fluid out through the outlet valve; and use pressure generated in the expansion chamber during the exhaust stroke, after closure of the exhaust valve at a point in the exhaust stroke, to apply an outward force to the inlet valve to assist in opening the inlet valve. In some embodiments, the pressure generated in the expansion chamber during the exhaust stroke is greater than the pressure at the inlet on a side external to the expansion chamber.

In some embodiments, the valve operating system includes an inlet cam that facilitates opening of the inlet valve, and, during operation, the applied outward force on the inlet valve reduces the opening force on the inlet cam.

In some embodiments, the applied outward force reduces the opening force on the inlet cam to less than 50%, 75%, 90%, or 95% (e.g., in the range of about 50% to about 100%, or any subrange thereof) of the force that would be required for opening in the absence of the applied outward force.

In some embodiments, during operation, the opening of the inlet valve is accomplished using only the outward force to the inlet valve.

In some embodiments, the inlet valve does not have an associated opening cam.

In some embodiments, where the inlet valve includes one or more mechanical latches, where: at least one mechanical latch is configured to hold the inlet valve in a stable open or a stable closed position during at least a portion of an operating cycle of the expansion device.

In some embodiments, during operation, the expansion device is configured to: during a first portion of the operating cycle, use the internal pressure of the expansion chamber to move the inlet valve outward towards a fully open position; and use at least one mechanical opening latch to hold the in the fully open position.

In some embodiments, during operation, the expansion device is configured to: use the operation of the opening latch to provide a force which assists in moving the inlet valve towards the fully open position.

In some embodiments, the inlet valve includes a mechanical latch and a spring mechanism, configured such that: during a first portion of an operating cycle of the expansion device, the mechanical latch maintains the inlet valve in a closed position; and during a second portion of the operating cycle, the latch is released and pressure inside the expansion chamber opens the inlet valve.

Some embodiments include: a spring mechanism configured to return the inlet valve from the open position to the closed position.

In some embodiments, the inlet valve is configured to be opened using the pressure inside the expansion chamber without the assistance of a force from an opening mechanism located external to the expansion chamber.

In some embodiments, the inlet valve includes at least one electromagnet, and the valve drive system is configured to: control the electromagnet to actuate the inlet valve between a substantially stable open position and a substantially stable open position.

In some embodiments, at least one electromagnet includes at least at least a first and a second electromagnets, and the valve drive system is configured to:: switch the first electromagnet to an on state and the second electromagnet to an off state to maintain the inlet valve in the stable open position; and switch the first electromagnet to an off state and the second electromagnet to an on state to maintain the inlet valve in the stable closed position.

In some embodiments, the inlet valve includes an over-center toggle mechanism having a stable closed and a stable open position, and the expansion device is configured to: during a first portion of the operating cycle of the expansion device, use the internal pressure of the expansion chamber to toggle the inlet valve from the stable closed position to the stable open position.

In some embodiments, the expansion device is configured to: during a second portion of the operating cycle, using a mechanism external to the expansion chamber to toggle the inlet valve into the stable closed position.

In some embodiments, the mechanism external to the expansion chamber includes at least one selected from the list consisting of: a cam, a mechanical actuator, a hydraulic actuator, and an electromechanically actuator.

In some embodiments, the inlet valve includes a spring loaded cam driven toggle mechanism, and where the valve drive system is configured to: place the valve in a closed position by seating a valve body against a seal, thereby causing a build up of pressure in the inlet to the expansion chamber; and rotate a cam to drive the toggle mechanism to apply an opening force on the valve body to unseat it from the seal, thereby placing the expansion chamber in fluid communication with the inlet and causing a reduction in inlet pressure.

In some embodiments, the force applied on the cam by the toggle mechanism is less than 20%, 10%, 5%, 1%, or less (e.g., in the range of 0-30%, or any subrange thereof) of the opening force applied to the valve body by the toggle mechanism.

In some embodiments, the reciprocating expansion device includes: a primary expansion chamber with a primary reciprocating element, and a secondary expansion chamber with a secondary reciprocation element, and is configured to use fluid exhausted from the primary expansion chamber to drive the operation of the secondary expansion chamber.

In some embodiments, the expansion chamber and reciprocating element include a cylinder with a piston.

In some embodiments, the reciprocating expansion device includes at least four piston cylinders.

In some embodiments, the working fluid at the inlet includes a supercritical working fluid.

Some embodiments include a system for implementing at least one thermodynamic trilateral flash cycle at least in part using the reciprocating expansion device.

Some embodiments include a system for implementing at least two cascaded thermodynamic cycles at least in part using the reciprocating expansion device.

In some embodiments, the expansion device is configured to extract mechanical work from expansion of the working fluid with an efficiency of at least 90%, 95%, 97%, or more (e.g. in the range of about 75% to about 100%, or any subrange thereof) of the thermodynamic limit.

In some embodiments, the expansion device is configured to extract mechanical work from expansion of the working fluid with an efficiency of at least 95% of the thermodynamic limit.

In some embodiments, the expansion device is configured to do work at the at least 0.1, 0.5. 1.0, or 10.0 megawatts (e.g. in the range of 0.01-100 megawatts or any subrange thereof).

In some embodiments, at least one inlet valve includes a poppet valve.

Various embodiments may include an of the above features, elements, steps, or techniques, either alone or in any suitable combination.

DESCRIPTION OF THE DRAWINGS

FIG. 1A and FIG. 1B show views of a desmodromic or positive opening positive opening cam and valve train. In each figured the left pane is a head on view, while in FIG. 1A the right pane is a top down view, and in FIG. 1B the right pane is a side view.

FIG. 2 illustrates lifting or upward opening twin inlet valve.

FIG. 3 illustrates upward opening inlet valve positioned in cylinder block.

FIG. 4 is a pressure-volume diagram illustrating the operation of a cylinder using overcompression to assist or accomplish inlet valve opening.

FIG. 5 illustrates a mechanical latch pressure opened inlet valve.

FIG. 6 illustrates a mechanical profiled latch pressure opened inlet valve.

FIG. 7 illustrates an electromagnetic latching and valve assist system.

FIG. 8 illustrates an over-centre spring and toggle pressure operated inlet valve.

FIG. 9 illustrates a cam actuated toggle lifter.

FIG. 10 is an illustration of a heat engine device featuring cascaded cycles.

FIG. 11 depicts the upper thermodynamic cycle of the heat engine of FIG. 10 laid out on a steam T s diagram.

FIG. 12 depicts the upper thermodynamic cycle of the heat engine of FIG. 10 laid out on an organic fluid Pressure-Enthalpy diagram.

FIG. 13 is a schematic of an exemplary embodiment of a heat engine device featuring cascaded thermodynamic cycles as depicted in FIGS. 11 and 12.

FIG. 14 depicts a thermodynamic cycle featuring feed preheating laid out on a steam T s diagram.

FIG. 15 illustrates an exemplary heat engine corresponding to the thermodynamic cycle of FIG. 12.

FIG. 16 is a plot of efficiency versus temperature for the heat engine of FIG. 15.

FIG. 17 is an illustration of an exemplary heat engine suitable for use with a low grade heat source.

FIG. 17A is a plot of cycle efficiency as a function of heat source return temperature for an exemplary heat engine.

FIG. 17B. is an illustration of an exemplary heat engine suitable for use with a low grade heat source featuring a heat recuperator.

FIG. 17C is an illustration of an exemplary heat engine suitable for use with a low grade heat source featuring three expanders and heat recuperator.

FIG. 18 depicts the thermodynamic cycle of the heat engine of FIG. 17 laid out on an organic fluid T s diagram.

FIG. 18A is a schematic of the thermodynamic cycle of the heat engine of FIG. 17 accounting for imperfectly isentropic expansion.

FIG. 19 is an illustration of an exemplary heat engine suitable for use with a low grade heat source featuring a secondary cycle.

FIG. 20 depicts the thermodynamic cycle of the heat engine of FIG. 19 laid out on an organic fluid T s diagram.

FIG. 21 is an illustration of the secondary cycle of the heat engine of FIG. 19.

DETAILED DESCRIPTION

The examples presented below describe the operation of expansion chamber (e.g., piston cylinder) inlet and exhaust valves. For the sake of convenience and as is conventional in the art, in these example, a valve which opens by movement of a vale body element in a direction outward from the expansion chamber is referred to as an upward opening valve. A valve which opens by movement of a vale body element in a direction inward the expansion chamber is referred to as a downward opening valve. However, as will be understood by one skilled in the art, that the embodiments described herein are not limited to those where the valves must be oriented on the top side of the expander device (although in may typical applications, this will be the case). In various embodiments, any suitable orientation may be used which maintains the inward/outward orientation of the valves described in the examples below.

In some embodiments, the present invention includes desmodromic valve operating system which operates poppet valves within the cylinder heads of a piston and cylinder engine, where total number of pistons may vary from one to 24 or greater. Some embodiments may feature multiple stage expansion. For example, in the case of two stages of expansion, in some embodiments, the expander may include sets of four cylinders (e.g., as shown in FIGS. 1A and 1B), where there is one high pressure cylinder followed by three low pressure cylinders, with exhaust from high pressure cylinder being directs as inlet to the low pressure cylinders. In various embodiments, any suitable number of stages with any suitable number of associated cylinders may be used.

Referring to FIGS. 1A and 1B, in one embodiment, for each cylinder and piston (labeled Cyl 1 through Cyl 4) the valve operating system includes an inlet valve 100 which is lifted off it's seat 105, away from the cylinder and piston by a mechanism consisting of two cams primary cam 106 and conjugate cam 107. These cams respectively bear on two over and under rockers 101 and 102 respectively, which in turn act on the valve stem through lifter 108. The task of the primary cam 106 is to lift or open the valve 100 and that of the conjugate cam 107 is to close or place the valve 100 back on its seat 105.

A similar action is performed on the exhaust valve 200, however in the opposite direction. That is a corresponding primary cam 206 opens the exhaust valve 200 by lowering it towards the piston within the cylinder and the conjugate cam 207 closes it by raising it into it's seat, away from the piston. Note that the valve action described above are quite unlike those occurring in a conventional internal combustion (IC) engine, where both sets of valves open into the cylinder. Similarly the valve timing is also quite different as compared with a conventional IC engine.

The relative working modes of the inlet and exhaust valves can be clearly seen in FIG. 1B, where inlet valves 100 open upwards and the exhausts valves 200 open downwards, in a typical four cylinder engine valve train.

Some embodiments include the provision of more than one valve per cylinder for inlet purposes. FIG. 2 shows an embodiment where two inlet valves 109 are operated by a single primary cam 110 and conjugate cam 111 pair, through a bridge lifter 112 running in guides 113. In this manner more than one valve inlet (or, additionally or alternatively, exhaust) function per cylinder may be accommodated by a single desmodromic cam train. In the particular configuration shown twin inlet valves 113 are used in a high pressure cylinder with a single exhaust valve (not shown). In the same manner a twin exhaust valve set up 301 may also be fitted, resulting in a four valve system, e.g., as shown in FIG. 3. In various embodiments, any suitable number on inlet and exhaust valves for a given cylinder may be used. In typical embodiments, the larger the number of valves per intake or exhaust function the smaller the flow friction loss experienced.

In various embodiments, the valve drive system is configured to ensure proper operation of the upward and downward motion through the use of cams, without either excessive gap between the upward rocker and valve which would result in delay and impact or clearances being too close which would result in “binding” and imperfect closure or insufficient valve opening.

For example, in a four cylinder engine (e.g., an IC type engine) converted to expander type operation, the valve train configuration may be as shown in FIG. 1A and FIG. 1B. An upward opening inlet valve 100 or valves is accompanied by a downward opening exhaust valve 200 or valves, as shown. In the case of a desmodromic system, the opening and closing cams are configured to push upward on plunger 108, in the case of the inlet valve with the closing rocker 102 being out of contact and travelling in an upward direction, enabling the inlet valve 100 to travel upwards. As the peak point of the cam 106 contacts rocker 101, as shown, plunger 108 is caused to move upward, opening the inlet valve 100.

In a similar manner, once the peak in the opening cam 103 moves out of contact, the closing cam 107 is moving the closing rocker 102 in such a manner as to close the inlet valve 100. By suitably arranging the shapes of the opening cam 106 and closing cam 107 and the design of the corresponding contacting rockers 101 and 102, the inlet valve 105 is caused to open or lift off the valves seat and after the appropriate dwell angle, caused to close on to it's seat.

In various embodiments, an expander which includes a negative (outward) or upward opening inlet valve and a positive (inward) or downward opening exhaust valve is capable of achieving very high isentropic efficiencies, e.g., as shown in the pressure-volume (pV) diagram of FIG. 4.

In the case shown an expander designed for use with an organic working fluid is instead being operated on pressurized air. Starting at the right hand end, position 501 corresponds to Bottom Dead Center (BDC) of the piston, the pressure in the cylinder has dropped to it's minimum value (atmospheric pressure in this case) and the exhaust valve 200 is open. The process 501-502 is the exhaust stroke, where spent gases are expelled by upward movement of the piston.

The exhaust valve 200 closes at position 502. Note that in various designs, the choice of the position of 502 is completely discretionary. That is, in various embodiments, the point of exhaust valve closure may be varied, e.g., by adjustment of the exhaust cams, an opening cam and a closing cam. The portion 502-503 represents a recompression stroke, wherein pressure in the cylinder increases to equal or exceed the inlet pressure in the chamber above the inlet valve. Recompression with pressure increase above inlet pressure provides an advantage in that it can be actively utilized to open the inlet valve, independent of or in assistance to a cam and rocker or other external system.

The inlet valve closes at point 505 and an adiabatic expansion takes place from point 505 to BDC before the exhaust valve opens at BDC. By varying the position n of each closing cam against the opening cam it is possible to precisely vary the opening and closing positions for each valve.

In various embodiments, the thermodynamic cycle shown above may be tailored to the application at hand (e.g., based on a given inlet pressure). Iv various embodiments the cycle above may be used to extract work from the working fluid with efficiency approaching the thermodynamic limit, e.g., 80%, 90%, 95%, or 99% efficiency or more, e.g., in the range of 80-100% or any subrange thereof. These efficiencies may be exhibited at any suitable piston reciprocation speed, and at any suitable power capacity (e.g. 1 kW, 10 kW, 100, kW, 1 MW, or more, e.g., in the range of 1-100,000 kW or any subrange thereof).

Note that, although one particularly advantages example has been described above, in various embodiments, the thermodynamic cycle described above may be modified.

In some embodiments, initiation of opening of the inlet valve is carried out using a mechanical latch system, e.g., in which all upward movement of the inlet valve is provided by virtue of the compression pressure in the cylinder. In such a system a rotating or other latch is released as shown in FIG. 5, such that the inlet valve is free to move upward under pressure. There are several methods to cause the inlet valve to reseat on it's valve seat. In some embodiments, one may accelerate an opened valve downward using a spring which contacts the valve only at a certain point in it's upward movement. In some embodiments, one may move the valve downward using a rotating cam which has the sole function of moving the valve down onto it's seat.

In the embodiment shown in FIG. 5, a lower latch 201 holds the valve 100 in a stable closed position by contacting fixed spacer 203, as shown in the left hand diagram. Before Top Dead Center (TDC) of a piston stroke, the latch is withdrawn but valve remain closed due to pressure in valve chamber 205 being higher than the pressure in working cylinder 206. At or approaching TDC, the pressure in the working cylinder 206 is configured to rise above the pressure in inlet chamber 205, e.g., as shown in step 502-503 in FIG. 4. This may ensured by suitably choosing the exhaust valve closing point 502 in FIG. 4, in relation to the final clearance volume along step 503-504. For any given clearance volume 503-504, any desired pressure may be achieved in the clearance volume 503-654. Once valve 207 has moved upward due to overpressure in cylinder 206, latch 202 is activated in such a manner as to lock valve 207 in an upper, stable open position, against compression force in spring 2051.

In some embodiments, as shown in FIG. 6, the upper latch 202 in the embodiment in FIG. 4 has a profiled shape and is able to bear against an upper step 204 on the inlet valve 100, from the moment of valve opening. In this case the profiled shape of the latch promotes valve lifting and also holds valve open (left hand pane) until it is time to reseat (right hand pane).

Referring to FIG. 7, in some embodiments the opening and/or closing of the inlet valve 100 is facilitated to operate electromagnetically using two sets of electromagnets 301 and 302, which would latch and unlatch, depending on valve position and operations required. In one embodiment, the manner of operation would be as follows: Just before piston TDC, electromagnet 301 (holding valve 100 in a stable closed position) will be released and electromagnet 302 energized, such that magnet rider 303 will be attracted to the upper magnet disk 302. At the point in time where upward recompression force in cylinder below the valve reaches or exceeds pressure within inlet chamber, a net upward pressure force will act on the inlet valve 100 and it will be forced upward. At the same time, there will be a further attractive force upward exerted by the switched on electromagnet 302, further enhancing valve upward movement, until magnet rider 303 is locked against upper, energized electromagnet 302 in a stable open position. In this manner any penetration into the chamber which carries hot inlet fluid will be reduced or completely eliminated-

In a further embodiment of the invention, a toggle and off center spring arrangement (sometimes referred to as an over-centre toggle mechanism) is provided such that the valve 100 is stable in two positions, ON the seat and OFF the seat, see FIG. 8 (left pane is on seat, right pane is off seat). Two swing arms 401 and 402 are provided, tension spring 403 mounted off center such that its greatest extension occurs when both arms 401 and 402 are in line, with the valve slightly lifted off it's seat. Also, it provides a second stable position with the valve fully open, as shown in the right hand diagram. As such, the spring provides a positive closing of the valve onto it's seat, in the closed position in the left hand diagram. The plunger 404 is actuated through a hydraulic connection through base 405 and has two positions, a fully extended position (left hand pane) diagram and a retracted position (right hand pane) In various embodiments, any other suitable type of actuator may be used.

The mode of operation is as follows: When the piston below the inlet valve 100 reaches TDC, the designed overpressure in the cylinder (point 503 in FIG. 4) causes inlet valve 100 to lift off it's seat. The toggle 401, 402 and spring 403 is configured such that the toggle goes over-center, within a few millimeters of travel and completely lifts the inlet valve off it's seat, to the second stability position shown in the right hand diagram. The small hydraulic plunger of valve 100 is withdrawn to its retracted position well before TDC, as such free movement of the toggle to it's upper stability positions is enabled. Before the proper valve cutoff time, the hydraulic plunger in base 405 is activated to push down on the valve stem and overcome the upward holding force due to the off center spring. Once the hydraulic plunger downward movement pushes the valve 100 past the upper stability position, the spring 403 moves the system to it's second stable point, causing it to seat. Further seating force is provided by the pressure differential between inlet chamber pressure and the decreasing pressure in the cylinder.

In another embodiment of the valve operating mechanism a cam actuated toggle may be configured as shown in FIG. 8. The left hand pane shows the valve 100 in a closed position. The right hand pane shows the valve 100 in an open position. In this case a short valve opening of distance X is caused by a cam 1501 bearing on a toggle 1502 having a roller 1505. The valve 100 is kept closed by a spring 1503 applying a force to the roller 1505 of the toggle 1502. As the cam 1501 rotates, it actuates the toggle 1502, lifting and unseating the valve 100 by a distance X from its seat. As shown, the cam effective lift distance Z−Y>>X (e.g. 2, 3, 4, 5, 10, or more times X, e.g., in the range of 2-100 times X or any subrange thereof) and as such the total force exerted on the valve 100 is much greater than the force on the cam 1501. A mechanical advantage is created which enables the inlet valve 100 to be lifted against very high pressures in the inlet chamber, without relying on gas over-compression pressure in the cylinder.

The arrangement of FIG. 9 is advantageous in that it accommodates a reverse seating valve, and features a single cam design. In some embodiments, a high inlet pressure will force the valve onto its seat with large forces, e.g., more than about 1000 lbs. Once the valve is moved off of the seat, the pressure will drop significantly (e.g., by more than 50%, 60%, 70%, 80%, 90%, or more). Note that controlled valve closing can then be accomplished using the spring force from spring 1502 on the roller 1505, or, in some embodiments, another type of closing actuator may be used.

Expanders of the type described herein may be used in any suitable type of heat engine or any other system which includes and expander. For example, expanders of the type described herein may be used in conjunction with the devices, systems and methods described in any of the applications incorporated by reference above.

For example, one or more expanders of the type described herein may be employed in a system featuring cascaded thermodynamic cycles. Referring to FIG. 10, a heat engine device 4000 includes multiple cascaded thermodynamic cycles (two are shown). An upper cycle operating on a first working fluid accepts heat from a heat source at a first temperature T1, rejects heat at a second lower temperature T2, and yields work (e.g. mechanical work.) The lower cycle accepts heat rejected by the upper cycle at a temperature T3 less than or about equal to T2. The lower cycle rejects heat into the surrounding environment (or yet another lower cycle) at a lower temperature T4. Accordingly, the lower cycle generates useful work from rejected heat from the upper cycle that otherwise may have simply gone to waste.

In some embodiments, the first working fluid of the upper cycle has a relatively high boiling point, while the second working fluid of the lower cycle has a relatively low boiling point. For example, the first working fluid may be pressurized water/steam, while the second working fluid is a low boiling point fluid, e.g. an organic fluid such as HCFC 123 or HCFC 134a. In other embodiments, the organic working fluid may include organic ammonia, benzene, butane, isobutane, carbon tetrachloride, propane, R-245fa, R-245ca, toluene, or any other suitable fluid. Accordingly, the lower cycle is able to operate efficiently using the relatively low temperature heat rejected from the upper cycle.

FIG. 13 shows an exemplary heat engine device 5000 featuring upper and lower cascaded trilateral flash cycles. The upper cycle operates on a pressurized water/steam working fluid and is depicted in the temperature-entropy T-s steam table of FIG. 11. The lower cycle operates on a an organic HCFC 123 fluid pressure-enthalpy diagram of FIG. 12.

Considering first the upper cycle, in process 5-1, a liquid pump 1500 isentropically compresses the water working fluid to upper working pressure. In process 1-2, a heat exchanger 135 transfers heat from a primary heat source to the compressed water working fluid. As shown, the heat source is waste heat from a coal power station at 140 degrees C., which heats the compressed working fluid from a temperature of about 32 degrees C. to a temperature of 120 degrees C.

In process 2-3 the heated working fluid undergoes isentropic (reversible, adiabatic) expansion in an expander 1360, and is cooled to a temperature of 102 degrees C. As shown, expander 1360 is a reciprocating piston expander, and may incorporate any of the devices and techniques described herein. For example, expander 1360 may be of the type shown in FIGS. 1A and 1B.

In process 3-4 heat is recovered from the expanded water vapor exhausted from the expander and transferred to the HCFC 123 working fluid of the lower cycle using a heat exchanger 1510. In process 4-5 the water vapor working fluid exiting the heat exchanger 1510 is condensed back tot the liquid state using a steam vapor condenser 1370. Note that, in some embodiments, the heat rejected during this process may also be transferred to heat the lower cycle working fluid. The condensed water working fluid is then recirculated to the pump 1500 to begin the cycle anew.

Considering the lower cycle, this cycle of the heat engine operates as a conventional trilateral flash cycle on the HCFC 123 working fluid. In process 6-7 a liquid pump 1500 isentropically compresses the HCFC 123 working fluid to upper working pressure. In process, 7-8, the pressurized HCFC 12 working fluid is heated to a temperature of 82 degrees C. in heat exchanger 1510 using heat rejected from the upper cycle.

In process 8-9 the heated HCFC 123 working fluid undergoes isentropic (reversible, adiabatic) expansion in an expander 1390, and is cooled to a temperature of about 40 degrees C. As shown, expander 1390 is a reciprocating piston expander and may incorporate any of the devices and techniques described herein. For example, expander 1360 may be of the type shown in FIGS. 1A and 1B.

In process, 9-6 the expanded working fluid exhausted from the expander 1390 is condensed in fluid condenser 1400, rejecting heat into the surrounding environment. Note that in some embodiments, the heat rejected by the lower cycle may be used to drive a tertiary cycle, etc.

As shown, all of the mechanical output of both types of expanders, upper water/vapor based expander 1360 and lower low boiling point organic based expander 1390 is integrated into a common shaft 1520 which is then used to turn a single alternator 1530 to generate electrical energy.

In embodiments described herein, two trilateral flash cycles, the upper one using water and the lower using a working fluid with a lower boiling point, are cascaded for purposes of achieving higher efficiency. In a typical example, recovery useful energy from the waste heat of a coal power plant stack gas, input and output parameters were as follows:

Coal fired power station Capacity 1000 MW flue gas flow 2.40E+06 M³/hr Flue gas temp 140 Deg C. Energy in flue gas 89760 kJ/sec Efficiency 10% power output 13.464 MW

Therefore useful power generation from waste heat may be carried out using low grade heat sources, utilizing the proposed cascaded thermodynamic cycle

While in both exemplary cycles described above the working fluid was heated into the wet vapor region, in other embodiments, the working fluid in one or more cycle may be heated to a supercritical fluid state.

As will be understood by those skilled in the art, the described heat engines may be modified to employ and of the devices or techniques described herein or in the reference incorporated above. For example, the heating processes may include the injection of quantity of working fluid into a chamber (e.g. of a piston), and the introduction of energy (e.g. via concentrated solar energy directed through a transparent window in the chamber) to the quantity of working fluid to vaporize the fluid, as described in detail above. Any of the cycles may include multiple expanders and/or bypass preheating devices and techniques described in the applications incorporated by reference above.

The general class of liquid to vapor expansion cycles in the wet vapor and supercritical region with bypass constitute a new class of thermodynamic cycles and provides enhanced efficiency possibilities in a multitude of applications: fixed bypass ratio systems may be used in constant output applications such as geothermal power generation; and, variable bypass ratio systems may be considered for hybrid vehicle applications, wherein a low bypass ratio is used during cruising only to charge a battery at a high efficiency, with a momentary high bypass ratio used to produce higher power output for overtaking, etc.

In some embodiment, it is possible to recover heat by splitting the working fluid into two parts after a first expansion process, see FIGS. 14 and 15. In such a case, the cycle diagram is shown in FIG. 14.

The cycle process steps are as follows. In process 1-2 the working fluid is preheated by means of extracted working fluid from an expansion process, in heat exchanger 1310. In process 2-3 heat is added to the preheated working fluid from outside source in a heat exchanger. In process 3-4, a primary expansion of all of the working fluid occurs, e.g. in piston/cylinder expander 1120, which may include and of the expander devices and techniques described herein. As shown, the primary expansion is isentropic (i.e. reversible and adiabatic). In some embodiments, the primary expansion may take place in any other suitable type of expander, e.g. a turbine expander. In some embodiments, mechanical work extracted during the primary expansion process (e.g. from piston expander 1120) may be used for any suitable application, e.g. to drive the shaft of a generator (e.g. a linear generator as shown) to generate electrical energy.

The working fluid is then exhausted at point 4 and divided into two parts in the flow splitter 1290. A first portion of the working fluid, having a fluid fraction k where 0<k<1 is diverted into heat exchanger 1310, as a heating fluid used to preheat the working fluid as described above. In process 4-2′-1 heat is transferred in exchanger 1310 from the first portion (i.e. the diverted portion) of the working fluid to the condensed and pressurized working fluid moving from condenser 1030 through pump 1040.

A second portion of the working fluid, having fluid fraction 1−k, is sent to a second expander 1300. As shown expander 1300 is a piston expander, e.g., of the type described herein, but any other suitable expander (e.g. a turbine expander) may be used. In process 4-5 the second portion of the working fluid undergoes further expansion to the condition at the fluid condenser 1030 denoted as point 5, with production of additional work. In process 5-6 the second portion of the working fluid is condensed in the condenser 1030.

In process 6-6′ the first (diverted) and second (undiverted) portions of the working fluid are mixed at the suction entrance to the pump. In process 6-1 the combined fluid is pressurization by the pump, and is ready to be recirculated to start new cycle

By utilizing a fraction k of the working fluid to preheat all of the working fluid, a significant efficiency gain is achieved in the thermodynamic cycle. Not wishing to be bound by theory, the inventors have found that the overall cycle efficiency may be calculated by the formula:

${Efficiency} = \frac{\left( {{h\; 3} - {\left( {1 - k} \right)h\; 5}} \right) - {h\; 4\mspace{11mu} k}}{\left( {{h\; 3} - {h\; 2}} \right)}$

Where h3 is enthalpy at point 3, h5 is enthalpy at point 5, h2 is the liquid enthalpy at point 2, h4 is the liquid vapor mix enthalpy at point 4, k is the fraction of working fluid diverted to be used in preheating, and T4 is the temperature at point 4. This simple but elegant formula provides a convenient method of calculating ideal cycle efficiency.

FIG. 16 shows an efficiency curve as a function of temperature T4 for a high pressure cycle with fluid extraction. In this case the temperature T4 is the intermediate temperature after the first expansion in expander 112, The basic cycle parameters are as follows:

Cycle top temperature T3 600 Deg C. Cycle Max pressure p3 300 bar a Condensing temperature T5 40 Deg C. Base efficiency w/o extraction 43% (dashed line in graph)

Notably, as shown in FIG. 16, the efficiency of the cycles is improved relative to a cycle without extraction for preheating over a wide range of intermediate temperatures T4.

A cycle of this type may have it's highest temperature and pressure point in the supercritical or subcritical region, in FIG. 14, the presentation is given in the subcritical region. As described in detail below, a similar construction is applicable in the supercritical region. The cycle is highly advantageous in that the primary heat exchanger providing “heat input” and the condenser 1030 may both be much smaller than in a comparable Rankine cycle, also a higher efficiency is achieved with just one stage of extraction type feedheating. In typical applications, a Rankine cycle requires six to nine or more stages of extraction feedheating, to achieve high efficiencies.

Referring to FIGS. 17, an exemplary heat engine 2000 suitable for use with a low grade heat source (for example at a temperature of less than 250 degrees C., less than 200 degrees C., or even less, e.g. in the range of 150-250 degrees C.) is illustrated. The corresponding thermodynamic cycle diagram for the heat engine 2000 is shown in FIG. 18. As with the embodiment shown in FIGS. 14 and 15, the heat engine 2000 recovers heat for feed fluid preheating by splitting the working fluid into two parts after a first expansion process. However, the heat engine 2000 preferably operates on an working fluid (e.g. an organic fluid) having a relatively low critical point temperature, for example less than 250 degrees C., less than 200 degrees C., less than 175 degrees C., less than 150 degrees C., or even less. In some embodiments, the working fluid critical temperature is in the range of 150 to 200 degrees C. As detailed below, such a low critical point working fluid may be readily heated to a supercritical state prior to expansion using heat from a low grade source.

Referring to FIG. 17, the heat engine includes a heat exchanger 2010 for transferring sensible heat from an incoming fluid (e.g. heated water from a collector field) to the pressurized cycle working fluid (as shown, organic working fluid R-245fa having a critical temperature of about 154 degrees C.). As shown the incoming fluid is at a temperature T=190 degrees C. This heat transfer is represented in FIG. 18 as process 1-2. As shown, the pressurized fluid is heated from a liquid state to a supercritical fluid state at a temperature T₂=180 degrees C.

The heated supercritical working fluid undergoes an isentropic expansion process 2-3 in the first high pressure expander 2020 (e.g., of any of the types described herein). As shown the first expander is a turbine expander, but any suitable expander (e.g. a reciprocating piston expander of the type described above) may be used. Work W_(hp) (e.g. mechanical work) is extracted during the expansion process. Referring to FIG. 18, note that the saturated vapor states of the organic working fluid has a region of positive gradient. Accordingly, the working fluid R-245fa becomes progressively drier during expansion process 1-2. As will be understood by those skilled in the art, this is advantageous, e.g., in that smaller, less costly expanders may be used to expand a relatively dry vapor than would be required to expand a wet vapor.

The working fluid exhausted from the first expander 2020 enters a flow splitter 2030 which directs a first portion of the working fluid to second low pressure expander 2040, as indicated by process 3-4. The flow splitter 2030 directs a second portion of the working fluid to bypass the second expander 2040, as indicated by process 3-6.

The first portion of the working fluid undergoes an isentropic expansion process 4-5 in the second low pressure expander 2050. As shown the first expander is a turbine expander, but any suitable expander (e.g. a reciprocating piston expander of the type described above) may be used. Work W_(lp) (e.g. mechanical work) is extracted during the expansion process. As in the first expansion process, the working fluid becomes progressively drier, which, in some embodiments, may advantageously allow for the use of smaller, less costly expanders.

In some embodiments, mechanical work extracted from the first and second expanders 2020 and 2040 may be used to drive a common shaft, e.g., which may in turn drive a generator to produce electrical energy. In other embodiments, the work generated by each of the expanders may be directed to separate applications.

Each of the first and second expanders may have expansion ratios greater than 1:1, 2:1:4:1, 8:1; 12:1 or more, e.g. in the range of 4:1 to 8:1 or 4:1 to 12:1 or any other suitable value. In some embodiments the expansion ration of the first expander may be greater than less than or equal to that of the second expander.

The first portion of the working fluid exhausted from the second expander 2040 is directed to condenser 2050. The condenser condenses the expanded vapor back to a liquid or substantially liquid state in process 5-7. The condenser rejects heat to the surrounding environment (as shown at temperature T₇=45 degrees C.).

The condensed first portion of the working fluid is directed to the first low pressure pump 2060, which isentropically pressurized the condensed fluid. The pressurized fluid is them mixed with the second portion of working fluid that was diverted to bypass the second low pressure expander 2040. The first and second portions of the working fluid are mixed in direct contact heat exchanger 2070 (point 6 in FIGS. 17 and 18). The second portion of the working fluid is at a higher temperature than the first portion, and thus operates to preheat the first portion, as shown in process 8-9.

In process 9-10 the combined fluid is pressurization by the second high pressure pump 2080. In process 10-1, the mixed, preheated, pressurized working fluid is recirculated to start new cycle.

A cyclic power generation process of this type with heat acceptance at a higher temperature and heat rejection at a lower temperature is governed by the Second Law of Thermodynamics and the maximum possible efficiency is the Carnot efficiency which is 1−T2/T1 where T1 and T2 are absolute temperatures of the heat source (e.g. the temperature of incoming water) and heat sink (i.e. the temperature in the condensing process 5-7) respectively. For the general conditions given in FIG. 18, Carnot efficiency is 31.3%. The other performance values for this exemplary embodiment are shown in the chart below.

Temperature of Source 190 C. Cycle Maximum temperature 180 C. Cycle heat rejection temperature 45 C. Bypass ratio 0.5 Ambient temperature 30 Deg C. (average) Isentropic efficiency 80% Net Cycle Efficiency 17% Specific Net work output 23 kJ/Kg

An isentropic or expander efficiencies of 80% or more are achievable for organic fluids such as R-245fa. Because these fluids become drier as expansion proceeds, the expansion process can proceed to temperatures near ambient without the fluid becoming two-phase. This avoids the complications of and the reductions in expander efficiency of operation in the two phase region. Therefore utilizing this type of fluid leads to a high cycle efficiency. Suitable fluids include organic ammonia, benzene, butane, isobutane, carbon tetrachloride, HCFC 123, HCFC 134a, propane, R-245fa, R-245ca, toluene, or any other suitable fluid.

Not wishing to be bound by theory, the inventors have found that a formula for the theoretical efficiency η for this type of cycle may be derived, as:

$\eta = {1 - {\frac{T_{c}}{T_{i\; n} - T_{out}}{\ln \left( \frac{T_{i\; n}}{T_{out}} \right)}}}$

Where T_(c) is the temperature at which the cycle rejects heat (i.e. T₇ as shown in FIG. 17), T_(in) is the temperature of the heat source (T_(A) as shown in FIG. 17), and T_(out) is the temperature at which fluid is returned to the heat source (T_(B) as shown in FIG. 17). FIG. 17A shows a plot of ideal efficiency η for the cycle shown in FIG. 17 as a function of T_(out). As T_(out) increases from a value of T_(out)=T_(c)=45 degrees C. to a value of T_(out)=T_(in)=190 degrees C., the ideal efficiency is seen to increase approximately linearly from about 17% to about to Carnot efficiency of 31%. In general, the ideal efficiency η may be used as a figure of merit to evaluate the performance of a given thermodynamic cycle.

The above formula for cycle efficiency assumes a perfectly isentropic (i.e., reversible) expansion process (i.e. process 2-5 as shown in FIG. 18) However, a modified formula may be used to calculate the efficiency of a cycle where the expansion process is not perfectly isentropic.

The isentropic efficiency η_(isent) for any gas expansion process, may be defined as the actual enthalpy change divided by ideal enthalpy change possible in the process and applies to reversible, adiabatic processes. FIG. 18A shows a modification of a thermodynamic cycle of the type shown in FIG. 18 to include some irreversibility in the expansion process. On the T-s diagram as shown, the vertical solid line T_(in)−T_(c) is an isentropic expansion line, and the dashed line is an imperfect expansion line, such that the ratio of the enthalpy differences is the isentropic efficiency. The temperature after irreversible expansion is Tout′ and temperature after partial heat recovery is T_(out)″.

Ideally, the total amount of heat available for recovery, represented as a temperature difference, is (T_(out)′−T_(out)). However, this whole amount may not available due to imperfect heat exchanger efficiencies. In such cases, the actual heat recovered is may represented by the difference between T_(out)″ and T_(out), given by (T_(out)″−T_(out)) where

$k = \frac{\left( {T_{out}^{''} - T_{out}} \right)}{\left( {T_{out}^{\prime} - T_{out}} \right)}$

Therefore k is a proportionality factor, where 0<k<1, which accounts for less-than-perfect heat recovery in an actual heat exchanger.

Taking into account the isentropic expansion efficiency η_(isent) and the heat recovery factor k, the cycle efficiency η may be calculated as:

$\eta = {1 - {\frac{T_{c}}{F\left( {T_{i\; n} - T_{out}} \right)}{\ln \left( \frac{T_{i\; n}}{T_{out}} \right)}} - {\left( {1 - \eta_{isent}} \right)\left( {1 - k} \right)}}$ where F = ((1 − k) + k η_(isent)).

Note that for the special case k=1 and n_(isent)=1, the above efficiency formula reduces to that derived in the case of perfect expansion efficiency and heat recovery.

As will be understood by those skilled in the art, the above described heat engines may be modified to employ and of the devices or techniques described herein. For example, the heating process 1-2 may include the injection of quantity of working fluid into a chamber (e.g. of a piston), and the introduction of energy (e.g. via concentrated solar energy directed through a transparent window in the chamber) to the quantity of working fluid to vaporize the fluid, as described in detail above.

Although in the examples above, 50% of the working fluid was diverted to bypass the second expander 2040, any other suitable bypass ratio may be used. In some embodiments, the bypass ratio may be adjust to improve or maximize one or more operating parameters of the cycle (e.g. net cycle efficiency, work output, etc.). In various embodiments, one or more of these operating parameters may be monitored via a suitable sensor, and the bypass ratio adjusted based on the sensor measurement (e.g. using a servo loop in real time).

In some embodiments, heat engine 2000 may be modified to include one or more additional components. For example, referring to FIG. 17B, in one embodiment a further modification of the cycle of FIG. 17 as described above incorporates another heat exchanger, called a recuperator 2090, to recover additional heat after the end of the expansion process in the second expander 2040. The heat engine cycle is identical to that shown in FIG. 17, except that the fluid at point 5, instead of being sent directly to the condenser 2050, is first diverted through recuperator 209, for transfer of residual heat to the fluid stream after condensation and prior to direct contact heat exchanger 207 (processes 5-5A and 8-8A). The temperature at point 5 is higher than condensing temperature at 5A and hence heat may be usefully recovered. In this manner additional heat recovery is facilitated, leading to increase in cycle efficiency over and above cycle in FIG. 17.

The calculated efficiency the heat engine 2000 depicted in FIG. 17B for a variety of exemplary operating parameters is given in the table below (all temperatures are in degrees C.). The table shows cycle efficiencies for various values of the efficiency of the following cycle components: the recuperator 2090, the pumps 2060 and 2080, and the expanders 2020 and 2040.

Working Fluid R245fa Pump C. Cycle Recuperator effi- Expander C. C. Ambient effi- efficiency ciency efficiency T₂ T₇ Temp. ciency 0.9 0.8 0.6 200 45 35 0.1491 0.9 0.8 0.7 200 45 35 0.1755 0.9 0.8 0.8 200 45 35 0.2008 0.9 0.8 0.9 200 45 35 0.2249 0.95 0.8 0.6 200 45 35 0.151 0.95 0.8 0.7 200 45 35 0.1776 0.95 0.8 0.8 200 45 35 0.2029 0.95 0.8 0.9 200 45 35 0.2271 0.95 0.8 0.6 200 40 35 0.1582 0.95 0.8 0.7 200 40 35 0.1854 0.95 0.8 0.8 200 40 35 0.2113 0.95 0.8 0.9 200 40 35 0.2359 0.9 0.8 0.6 200 40 35 0.1561 0.9 0.8 0.7 200 40 35 0.1832 0.9 0.8 0.8 200 40 35 0.209 0.9 0.8 0.9 200 40 35 0.2337

Generally the incorporation of both feed water heating and recuperation after final expansion has result in a significant practical cycle efficiency improvement. Note that cycle efficiencies of greater than 17%, e.g., up to about 24% or more may be achieved. In some embodiments, the efficiency may approach the theoretical Carnot efficiency (equal to 1−T₂/T₇). In some embodiments, the cycle efficiency may be in the range of about 15% to about 25%.

Referring to FIG. 15C, in one embodiment, heat engine 2000 includes a third, still lower pressure expander 2100 (e.g., of any of the types described herein) positioned after low pressure expander 2040. A second flow splitter 2030A is positioned between expanders 2040 and 2100. Flow splitter 2030A directs a portion of the working fluid exiting the second expander 2040 to bypass the third expander 2100. This portion of the working fluid is directed to feed water heater 2070A, to direct contact heat exchanger 2070A, which is paired with pump 2080A.

As will be evident to one skilled in the art, any number of additional heat expanders may be included in a similar fashion, each capable of extracting mechanical work Flow splitters positioned between some or all of the expanders to allow extraction of working fluid to be used for feed fluid heating.

The calculated efficiency the heat engine 2000 depicted in FIG. 17C for a variety of exemplary operating parameters is given in the table below (all temperatures are in degrees C.). The table shows cycle efficiencies for various values of the efficiency of the following cycle components: the recuperator 2090, the pumps 2060, 2080 and 2080A, and the expanders 2020, 2040, and 2100.

Generally the incorporation of both feed water heating and recuperation after final expansion has resulted in a significant practical cycle efficiency improvement. Note that cycle efficiencies of greater than 17%, e.g., up to about 24% or more may be achieved. In some embodiments, the efficiency may approach the theoretical Carnot efficiency (equal to 1−T₂/T₇). In some embodiments, the cycle efficiency may be in the range of about 15% to about 25%.

recup Pump T2 T7 T eff eff Exp eff cycle cycle ambient Cyc eff 0.9 0.8 0.6 200 45 35 0.1514 0.9 0.8 0.7 200 45 35 0.1774 0.9 0.8 0.8 200 45 35 0.2024 0.9 0.8 0.9 200 45 35 0.2266 0.95 0.8 0.6 200 45 35 0.1533 0.95 0.8 0.7 200 45 35 0.1793 0.95 0.8 0.8 200 45 35 0.2044 0.95 0.8 0.9 200 45 35 0.2283 0.95 0.8 0.6 200 40 35 0.1606 0.95 0.8 0.7 200 40 35 0.1875 0.95 0.8 0.8 200 40 35 0.2133 0.95 0.8 0.9 200 40 35 0.2381 0.9 0.8 0.6 200 40 35 0.1587 0.9 0.8 0.7 200 40 35 0.1856 0.9 0.8 0.8 200 40 35 0.2114 0.9 0.8 0.9 200 40 35 0.2362

Referring to FIGS. 19 and 20, in some embodiments the heat engine 2000 may be modified to include a secondary thermodynamic cycle heat engine (labeled C) which converts the thermal energy from the diverted second portion of the working fluid to other form of energy (e.g. mechanical work). As shown, heat exchanger 3010 transfers heat at a first temperature (e.g. about 100 deg C.) from the diverted fluid to drive cycle C to generate mechanical work W_(C). Cycle C rejects heat to the surrounding environment at a lower temperature (e.g. 45 degrees C.).

As will be understood by one skilled in the art, an increased amount of mechanical work extracted from the diverted fluid will lead to a decreased cycle efficiency for heat engine 2000. Referring to FIG. 20, the dashed arrows indicate the operation of the cycle of heat engine 2000 at different values of work extracted. As more work is extracted, less feed fluid preheating is provided by the diverted fluid, leading to a decrease in cycle efficiency. Suitable values for the amount of extracted work can be selected based on the application at hand.

FIG. 21 shows a more detailed view of an exemplary embodiment of secondary cycle C. As shown, cycle C is a single expander trilateral flash cycle. In process 1-2, the second portion of working fluid from the primary cycle transfers heat to the working fluid of secondary cycle C. In the example shown, the incoming fluid is at a temperature of 130 degrees C., and heats the working fluid to a temperature of 120 degrees C. In process 2-3, the heated working fluid is directed to an expander (a piston or turbine expander). In process 3-4, the heated working fluid undergoes isentropic expansion in the expander to yield mechanical work. In process 4-5, the expanded working fluid is condensed, rejecting heat to the surrounding environment at a temperature of 45 degrees C. In process 5-6, the condensed working fluid is repressurized, and in process 6-1 the repressurized fluid is recirculated to start the cycle anew.

Although FIG. 21 shows a trilateral flash cycle, any suitable thermodynamic cycle may be used to extract mechanical work from the second portion of the working fluid of heat engine 2000. Other heat engine types include a Stirling cycle, a Rankine cycles, or any of the cycles described herein. The cycles may use any suitable organic or inorganic fluid, including any of the working fluids described herein. In various embodiments the working fluid can be heated to a state in the liquid-vapor region, or in the supercritical region.

Various example have been presented of expanders and thermodynamic cycles which operate without combustion or other substantial energy generating chemical reaction involving the working fluid. However, it is to be understood that in some embodiments, combustion or other chemical reactions may be used.

Although a number of particularly advantageous examples have been given above featuring piston cylinder type reciprocating expanders, it will be understood that other expanders, e.g., other types of reciprocating expanders may be used. Some embodiments may use scroll type expanders, or other expander types known in the art.

The scope of the present invention is not limited by what has been specifically shown and described hereinabove. Those skilled in the art will recognize that there are suitable alternatives to the depicted examples of materials, configurations, constructions and dimensions. Numerous references, including patents and various publications, are cited and discussed in the description of this invention. The citation and discussion of such references is provided merely to clarify the description of the present invention and is not an admission that any reference is prior art to the invention described herein. All references cited and discussed in this specification are incorporated herein by reference in their entirety.

While various inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the inventive teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure.

The above-described embodiments can be implemented in any of numerous ways. For example, the embodiments may be implemented using hardware, software or a combination thereof.

Also, various inventive concepts may be embodied as one or more methods, of which an example has been provided. The acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments.

All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms.

Variations, modifications and other implementations of what is described herein will occur to those of ordinary skill in the art without departing from the spirit and scope of the invention. While certain embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the spirit and scope of the invention. The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as a limitation. 

What is claimed is:
 1. A method of operating a reciprocating expansion device, the expansion device comprising at least one expansion chamber with a reciprocating element, a inlet to the expansion chamber with at least one outward opening inlet valve, and an exhaust from the expansion chamber having at least one inward opening outlet valve, the method comprising: providing pressurized working fluid to the inlet; opening the inlet valve in the outward directed to deliverer pressurized working fluid to the expansion chamber to expand and to drive a motion of the reciprocating element; and opening the outlet valve in the inward direction to allow expanded working fluid to escape the expansion chamber to the exhaust.
 2. The method of claim 1, further comprising: opening and closing the inlet and outlet valves using a desmodromic cam device, said cam device applying force during both opening and closing movements of the inlet and outlet valves.
 3. The method of claim 2, wherein each of the inlet and outlet valves is opened and closed without the use of a spring closure mechanism.
 4. The method of claim 1, comprising: using an exhaust stroke of the reciprocating element to drive expanded working fluid out through the outlet valve; and using pressure generated in the expansion chamber during the exhaust stroke to apply an outward force to the inlet valve to assist in opening the inlet valve; wherein the pressure generated in the expansion chamber during the exhaust is greater than the pressure at the inlet on a side external to the expansion chamber.
 5. The method of claim 4, wherein the applied outward force on the inlet valve reduces an inlet valve cam opening force on a cam used to open the inlet valve.
 6. The method of claim 5, comprising generating pressure in the cylinder to a required value by controlling of the point of closure of the exhaust valve.
 7. The method of claim 4, wherein the opening of the inlet valve is accomplished using only the outward force to the inlet valve, generated by a recompression pressure in the cylinder.
 8. The method of claim 7, wherein the inlet valve does not have an associated opening cam.
 9. The method of claim 1, wherein the inlet valve comprises one or more mechanical latches, the method comprising: using at least one mechanical latch to hold the inlet valve in a stable open or a stable closed position during at least a portion of an operating cycle of the expansion chamber.
 10. The method of claim 9, comprising: during a first portion of the operating cycle, using the internal pressure of the expansion chamber to move the inlet valve outward towards a fully open position; using at least one mechanical opening latch to hold the in the fully open position.
 11. The method of claim 10, comprising: using the operation of the opening latch to provide a force which assists in moving the inlet valve towards the fully open position.
 12. The method of claim 1, wherein: the inlet valve comprises a mechanical latch and a spring mechanism, and wherein the method comprises: during a first portion of an operating cycle of the expansion chamber, using the mechanical latch to maintain the inlet valve in a closed position; during a second portion of the operating cycle, releasing the latch, and using pressure inside the expansion chamber to open the inlet valve; and using the spring mechanism to return the inlet valve from the open position to the closed position.
 13. The method of claim 10, wherein the inlet valve is opened using the pressure inside the expansion chamber without the assistance of a force from an opening mechanism located external to the expansion chamber.
 14. The method of claim 1, wherein the inlet valve comprises at least one electromagnet, the method comprising: controlling the electromagnet to actuate the inlet valve between a substantially stable open position and a substantially stable open position.
 15. The method of claim 14, wherein the at least one electromagnet comprises at least a first and a second electromagnets, the method comprising: switching the first electromagnet to an on state and the second electromagnet to an off state to maintain the inlet valve in the stable open position; and switching the first electromagnet to an off state and the second electromagnet to an on state to maintain the inlet valve in the stable closed position.
 16. The method of claim 1, wherein the inlet valve comprises an over-center toggle mechanism having a stable closed and a stable open position, wherein the method comprises: during a first portion of the operating cycle of the expansion chamber, using the internal pressure of the expansion chamber to toggle the inlet valve from the stable closed position to the stable open position.
 17. The method of claim 16, further comprising: during a second portion of the operating cycle, using a mechanism external to the expansion chamber to toggle the inlet valve into the stable closed position.
 18. The method of claim 1, wherein the inlet valve comprises a spring loaded cam driven toggle mechanism, the method comprising: placing the valve in a closed position by seating a valve body against a seal, thereby causing a build up of pressure in the inlet to the expansion chamber; and rotating a cam to drive the toggle mechanism to apply an opening force on the valve body to unseat it from the seal, thereby placing the expansion chamber in fluid communication with the inlet and causing a reduction in inlet pressure.
 19. The method of claim 1, wherein the reciprocating expansion device comprises: a primary expansion chamber with a primary reciprocating element, and a secondary expansion chamber with a secondary reciprocation element, the method comprising: using fluid exhausted from the primary expansion chamber to drive the operation of the secondary expansion chamber.
 20. An apparatus comprising a reciprocating expansion device comprising: at least one expansion chamber with a reciprocating element, an inlet to the expansion chamber with at least one outward opening inlet valve and configured to receive a pressurized working fluid, and an exhaust from the expansion chamber having at least one inward opening outlet valve; and a valve drive system configured to: open the inlet valve in the outward directed to deliver pressurized working fluid to the expansion chamber to expand and to drive a motion of the reciprocating element; and open the outlet valve to allow expanded working fluid to escape the expansion chamber to the exhaust. 